“These responses are the most impressive to me,” says Sulak, who practices at Maine Integrative Healthcare in Manchester. Maine is one of 20 states, along with the District of Columbia, where medical marijuana is legal. “With inflammatory bowel disease, we’ll see patients who were at death’s door turn around dramatically.”

Sulak’s experience is powerful and adds to the large body of personal stories -- dating from 5,000 years ago -- about the therapeutic value of marijuana.

But the scientific evidence behind the drug’s benefits remains elusive, even as 10 more states consider legalizing medical uses in 2014. The problem: In 1970, the federal government classified marijuana as an illegal, highly addictive drug with no medical value, making research harder to do.

A Marijuana Discovery

Here’s what is known: About 20 years ago, scientists discovered a system in the brain that responds to 60 chemicals in marijuana, also known as cannabis. It’s called the endocannabinoid system. This system plays a role in many of the body’s functions, such as in the heart, along with the digestive, endocrine, immune, nervous, and reproductive systems. The discovery sparked interest in finding specific chemicals made from marijuana that could be targeted for specific conditions.

Since that time, scientific projects around medical marijuana worldwide have sped up dramatically. Many of the studies that have been done show that chemicals in marijuana can help treat some conditions. They have helped manage pain and reduced muscle spasms in MS patients. They’ve worked as an appetite stimulant, and as an alternative drug for brain disorders such as schizophrenia and Tourette’s syndrome.

Few of these studies, though, followed a controlled clinical trial. This is considered the best type of trial because it compares a drug to another drug, or to a placebo (a "fake" treatment).